An experimental and numerical study of evaporite mineral dissolution and density-driven flow in porous media

Abstract

Subsurface mineral dissolution problems exhibit complex behaviors, which are difficult to model and validate numerically. Controlled, physically-validated experimental problems can be used to better understand mineral dissolution and subsequent numerical representation, bridging the gap between numerical models and field observations. The objective of this work was to collect the first controlled, physical measurements in a porous aquifer overlying an evaporite mineral, and to create a numerical model of the system. The problem studied was modified from the classic HYDROCOIN Level 1 Case 5 problem. Three flow gradients in a porous aquifer were investigated in duplicate in a 2-D box-problem. The duplicate measurements had high variability, shown by numerical modeling to be a result of initial conditions, variable flux representing dissolution, sharp gradients, and variable dispersivity. The physical measurements of parameters and fields were important for calibration success. The numerical models, including sensitivity analyses, were capable of simulating flow patterns, observed concentrations, and peaks resulting from observed initial conditions. The numerical models were a key tool in understanding factors influencing the flow and spread of salt within the system. The models were limited by the ability to detail physical observations, difficult in both the laboratory and for potential field applications. The results provided insight in the HYDROCOIN Level 1 Case 5 numerical simulations, with flow appearing to be swept-forward; however, observed concentrations were lower than commonly modeled.